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Old 5th December 2003, 10:33 AM   #1
Nuuk is offline Nuuk  United Kingdom
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Default Lack of gain?

I have asked this question in the loudspeakers section but will more likely find an answer here.

I am currently using a VBIGC, full details of which can be found HERE

I am sure that when I first used this amp, I could only use the first few positons on the volume control but now I need to have the volume control at nearly maximum for normal listening.

Yesterday, I put in some EQ for my open baffle speakers and found that I could hardly get any volume at all.

Click the image to open in full size.

Has anybody any ideas what has happened. The mystery is all the more puzzling as both channels are exactly the same!
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Old 5th December 2003, 10:46 AM   #2
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Can you tell me how you have calculated these cap values, because these seems totally wrong. What is your goal with them?
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Old 5th December 2003, 10:54 AM   #3
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Nuuk, what are you trying to do?
EQ?
It seams that those resistors and caps are making a heavy attenuatiion on the signal...
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Old 5th December 2003, 10:56 AM   #4
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Default Re: Lack of gain?

Quote:
Originally posted by Nuuk
I have asked this question in the loudspeakers section but will more likely find an answer here.

I am currently using a VBIGC, full details of which can be found HERE

I am sure that when I first used this amp, I could only use the first few positons on the volume control but now I need to have the volume control at nearly maximum for normal listening.

Yesterday, I put in some EQ for my open baffle speakers and found that I could hardly get any volume at all.

Click the image to open in full size.

Has anybody any ideas what has happened. The mystery is all the more puzzling as both channels are exactly the same!
first of all. Your 220nF across 9.1K make a lowpass filter. Wich starts to attenuates the signal 6dB/octave from 80Hz up to 13KHz where the attenuating start to flatten out at -47dB
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Old 5th December 2003, 11:34 AM   #5
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Default Re: Lack of gain?

Konnichiwa,

Quote:
Originally posted by Nuuk
Yesterday, I put in some EQ for my open baffle speakers and found that I could hardly get any volume at all.

Click the image to open in full size.

Has anybody any ideas what has happened.
You MESSED UP my instructions. The 220nF Cap and 9k1 Resistor are siupposed to be in SERIES, not parallel.

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Old 5th December 2003, 12:04 PM   #6
Nuuk is offline Nuuk  United Kingdom
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Quote:
You MESSED UP my instructions. The 220nF Cap and 9k1 Resistor are siupposed to be in SERIES, not parallel.
Oops, sorry KYW, we English are not taught the language so well as our overseas friends

I'll move that 0.22uF cap in series and try again. I still have the strange thing about the overall gain of the VBIGC though.
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Old 5th December 2003, 12:23 PM   #7
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Quote:
Originally posted by Nuuk

I'll move that 0.22uF cap in series and try again.

The cap AND the resistor.
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Old 5th December 2003, 12:27 PM   #8
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Nuuk,
I've looked to your VBIGC schematic, as posted on your site, and now I'm confused.
Don't you have a gain of 68 on your amp?
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Old 5th December 2003, 12:37 PM   #9
Nuuk is offline Nuuk  United Kingdom
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Quote:
The cap AND the resistor.
I'm confused now (what's new ) This is what T said:

Quote:
Resistor in series with signal = 12k
Resistor in series with capacitor to ground = 9K1 & 0.22uF

For a little treble lift try a 1nF Capacitor (or larger/smaller to taste) in parallel with the 12k Resistor.
The 9K1 resistor is already going to ground so I only need to move the 0.22uF cap in series with it rather than parallel - don't I?

Or is the 9K1 in series with the 12K?
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Old 5th December 2003, 05:55 PM   #10
Nuuk is offline Nuuk  United Kingdom
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Could somebody please confirm that this is the correct arrangement?

Click the image to open in full size.
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